The present invention relates to oscillator circuits and more particularly to a self-protecting transistor oscillator circuit.
In conventional transistor oscillator circuits, removal of the load from the oscillator increases the collector-to-emitter alternating voltage. This excess voltage can destroy the oscillating transistor. To avoid this problem, buffer circuits between the oscillator and load have been employed. Such buffer circuits increase cost and complexity of the equipment in which they are employed. The circuit of the present invention senses excessive load impedance, and turns itself off, protecting both the load and the transistors. In portable equipment, where the load is only connected to the oscillator output intermittently, expensive battery energy may be conserved if the oscillator circuit is shut down when not in use. In other relatively high power applications, such as employed in connection with inductive or dielectric heating, where the work is introduced into the electromagnetic field on an intermittent basis, it is desirable to cause the oscillator to shut itself off when the work is not in position for application of high frequency energy.